The present disclosure relates to wireless networking such as Long Term Evolution (LTE) networks. There is a need to provide mission-critical performance for certain services over LTE, such as, for example, in public safety applications. While LTE provides guaranteed bit rate unicast services, LTE does not provide mission-critical performance on the downlink for one-to-many services because there is no limit on the number of users that may need to receive a copy of the one-to-many service. The only way to guarantee a constant bit rate for all users on the downlink is to use broadcast. LTE provides a broadcast service called multimedia broadcast single frequency network (MBSFN) which is a communication channel in LTE which sends the same content information to all users in a cell (broadcast) or to a given set of users (subscribers) in a cell (multicast) using a subset of the available radio resources with the remaining available to support transmissions towards a particular user (so-called unicast services). MBSFN is a transmission mode which exploits LTE's Orthogonal frequency-division multiplexing (OFDM) radio interface to send multicast or broadcast data as a multicell transmission over a synchronized single-frequency network (SFN). This group of cells is called a “broadcast area”. The transmissions from the multiple cells in the broadcast area are sufficiently tightly synchronized for each to arrive at the UE within the OFDM Cyclic Prefix (CP) so as to avoid Inter-Symbol Interference (ISI). In effect, this makes the MBSFN transmission appear to user equipment (UE) as a transmission from a single large cell, dramatically increasing the Signal-to-Interference Ratio (SIR) due to the absence of inter-cell interference.
However, interference at the edge of a broadcast area can limit the bit rate that can be supported. Not only that, but since broadcast is used, the bit rate is limited for the entire broadcast area. Disadvantageously, a low modulation/coding selection has to be used to provide mission-critical reliability and the associated bit rate supported may be too low to provide enough channels. For example, in a public safety LTE system for a large police department, e.g. the NYPD, the bit rate supported would be too low to provide enough voice channels. Accordingly, there is a need for single-frequency network broadcast for mission-critical service on LTE.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.